In the prior art cutting device, protecting covers are used to enclose the knife portions so as to prevent the knife edges to be destroyed. However generally, the damage of the knife portions of a cutting means is due to the use of the cutting means (at this moment, the cover is taken out from the cutting device and thus no protection function is presented).
In use of a cutting means, if a great force is applied to the device, the knife portions will suffer the great force so as to wear or be damaged. However this will reduce the lifetime of the cutting device.
This is because in cutting, the two knife edges of the cutting device will resist against an object to be cut so that the great force will apply to the contact surfaces of the two knife edges. However for a longer time the contact surfaces will wear. Furthermore, this will induce the knife edges to shift from one another so that they can not be aligned in cutting. However this will induce that the object to be cut cannot be cut effectively.